Iran, Saudi Arabia, Syria and Turkey are all pursuing their agendas and taking sides along a Sunni-Shiite divide. That could become dangerous as U.S. troops withdraw.

Reporting from Baghdad — As U.S. troops accelerate their withdrawal from Iraq, a fierce and potentially dangerous struggle to fill the vacuum is gathering pace among the country's often bitterly opposed neighbors.

Already, the 5-month-old effort to form a new government has become snarled in the battle for influence, with rival nations lining up behind the factions and political leaders shuttling among neighboring capitals for talks with their patrons.

The jockeying isn't new, but many Iraqis worry that it could take on alarming new dimensions as U.S. troops pull out, leaving the country vulnerable to threats and pressure from predatory regional powers.

"It is very dangerous," Iraqi Foreign Minister Hoshyar Zebari said. "It's a zero-sum game for these countries. Everyone wants to knock down the other one's policy."

The battle's broad outlines mirror the Sunni-Shiite sectarian divide within Iraq, but it is more complicated than that, as a tour of Iraq's borders makes clear.

To the east is Iran, which is determined to see Iraq's Shiite Muslims sustain their dominant role in government and, by extension, maintain Tehran's expanded influence there. Iran wants to see an alliance of the two main Shiite factions: the one led by Prime Minister Nouri Maliki and the Iraqi National Alliance, which groups supporters of anti-American cleric Muqtada Sadr and the Supreme Islamic Iraqi Council.

To the south is Saudi Arabia, the self-appointed guardian of Sunni power, which is equally determined to check Shiite expansionism by backing the coalition led by former Prime Minister Iyad Allawi, a secular Shiite whose bloc is supported by Sunnis.

To the north, Turkey, with its restive Kurdish population, wants to block any moves toward independence by Iraq's Kurds, the potential kingmakers in any deal. Turkey also backs Allawi, and has forged close ties with Arab nationalists opposed to Kurdish separatism within his coalition.

And to the west is Syria, Iran's ally and Saudi Arabia's rival on most regional issues, but pursuing its own agenda in Iraq. Syria's Baathist regime backs Allawi, who has the support of former Iraqi Baathists, and last month it hosted a groundbreaking meeting in Damascus between Allawi and Sadr, an alliance that would suit neither Iran nor the United States.

Reflecting U.S. concern that Iraq will fall under foreign influence, especially that of Iran, Vice President Joe Biden on a recent visit to Baghdad urged Iraqis not to allow any external power, including the United States, to "dictate" their fate.

But the U.S. is a player too, albeit one whose influence is waning, and has its own interest in ensuring that the government is stable and aligned with America. To that end, it has been promoting an alliance between Maliki and Allawi that would bridge the Sunni-Shiite divide and win broad acceptance across the region.

U.S. officials have grown increasingly worried that a new government won't be in place before all combat troops withdraw and America's clout diminishes further. The Obama administration has stepped up its engagement, dispatching in recent days a team of experts and advisors to try to exert pressure on the factions.

The difficulty of reconciling these agendas goes some way toward explaining why the formation of the government is taking so long. With the United States, Turkey and the Arab states insisting that Allawi play a leading role and Iran determined to squeeze him out, the process is deadlocked.

"It's why we're stuck," said Izzat Shahbandar, a member of Maliki's coalition.

Powerful personalities, sectarian rivalries and conflicting political visions are also to blame, as is the finely balanced outcome of the election, which left each faction seeking coalition partners.

But whenever a potential alliance seems close, one regional power or another will step in to nix it. That happened when Saudi Arabia moved to block a budding Shiite-Kurdish alliance forged in Tehran that would have excluded Allawi: It invited all the major players to Riyadh, except Maliki. The meeting opened a channel between Allawi's bloc and the Iraqi National Alliance.

Iraq lies at a strategic crossroads between the Arab world and the rest of Asia, an entry point to the region for non-Arab powers such as Turkey and Iran and a line of defense for Saudi Arabia and the Arab gulf states. With the world's third-largest oil reserves and plans to dramatically boost production, the country also has the potential to be rich. All of its neighbors have a vital interest in ensuring that Iraq becomes an ally, and not an aggressor, as it was under Saddam Hussein.

But with Iraq's neighbors often at odds, there is a risk that the country will become the region's political football, in which conflicts are played out much in the way they are in tiny, unstable Lebanon.